Hydraulic control



H. s. PARDEE 2,279,176

y HYDRAULIC CONTROL l Filed July 51, 1940 .l l /9 b1 E# ,f5 @5 37m 22 I n if 9/ X I j( t 6 v PP /l Z Z6 22 A? l /3 f5 l i Z mi? 2/ 3f /9 /5 24 ,A/QWVS/M,

Patented: Apta?, 1942 UNITED STATES PATENT OFFICE ilogllijzn. 348.643

'4 Claims.

This invention relates to hydraulic system controis. and with regard to certain more speciiic features, to a control unit for a hydraulic pump circuit.

Among the several objects of the invention may be noted the provision of means for controlling pump pressure by simple and compact apparatus which also functions as a safety valve: and the provision of apparatus of the class Idescribed which is the equivalent in function to a variable-stroke pump, but without its intricacies.

Other objects will be in part obvious and' in part l pointed out hereinafter. y

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exempliiied in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing, in which is illustrated one ci' various possible embodiments of the invention:

Fig. l is a diagram showing the. application of the device to a hydraulic circuit;

Fig. 2 is a longitudinal section of the control per se shown in a position at the start of pumping;

Fig. 3 is a view similar to Fig. 2 showing conditions after a normal pressure has been reached; and.

the control in position to act as a safety valve at high pressures.

Similar reference characters indicate correspending parts throughout the several views of i is in communication with its suction port ST.

The purposeof the pump P is to withdraw fluid from the sump tank S (via ports ST and PS) and to deliver it to the pressure tank T (via ports PP and PT) for use in a circuit connected to the pressure tank T. 'I'he circuit is not shown. be-

cause it does not form a part of the present invention per se. It receives fluid from tank T and drains it back to S.

Referring to Figs. 2-4, numeral 8 indicates ai body portion of the pump control, which forms Fig. c is s view similar to Fig. 2 but showing' the ports PT, PP, PS and ST. A bushingv, having a central passage or interconnection l, serves to form a Acommunication between the ports PT and PP via. ports 9, li and the left end .of paslsage It also serves to form a connection between the ports PS .and ST via passages I3 in connection withv the right end ofthe passage 1. It will be seen that the passage l communicates withthe interior of the body 3 and that .therefore the space l5 also forms part of the last-specified connection.

Ports PP and ST may also be connected by the central part of passage l, which may be referred to as an interconnection.

At the left end of the passage l is a valve seat insert il with which cooperates a valve I9. Valve I9 is normally pressed tolits seat by a spring 2l held by a cap 2d. Parts Il, i9 and 2i form a check valve between the pump port PP and the pressure tank port PT, which opens in response to pressure directed from PP to PT. It will not permit reverse iiow, as when the pump is disconnected and the pressure tank T left connected.

It is to be understood that the check valve is optional, and that its primary function is to permit disconnection of the pump without relieving the pressure tank 'I' of pressure, that is, without reiiux from the tank T (acting as an accumulator) to the discharge connection4 of the pump. It also prevents ow between the pressure tank and the sump in the extreme right-hand or relief position of the plug 23. This plug will be described more fully hereinafter.

At 23 is shown a valve or control plug, having upper and lower' ilats 22, which slides in the passage l and, with 25, forms an extension of a control rod 25. The rod 2S is guided at 32 for true axial movement. 'I'he guide 32 is in an adjustable threaded bushing 28 forming a stationary reaction point for spring 3i. The other end of the spring acts against a shouldered abutment 3i carried on the stem 25. A cap 2 encloses the spring chamber. A cross opening 26 is provided on the end of abutment 33.

Operation is as follows:

When the pump P starts and tank T is under no internal pressure, the parts are in the condition shown in Fig. 2, wherein the plug 23 is pushed'to the left by the extended spring 3|. The right end of the plug 28 thus uncovers the port I3; as shown, and places the sump tank in communication with the pump via connected ports ST. right end of 1. 2e, i5 and PS.

'Ihen as the discharge Pressure from the pump is transmitted from the pressure pump port PP 2 tothe' pressure-tank port PT and into the tank T, this pressure increases and forces the plug 23 to the right, thus compressing spring 3| (Fi 3).

lginally, when under a chosen value of moderate or normal pressure conditions the plug 23 covers the port I3, the suction side of the pump is cut off from the sump tank (ports ST and PS out oi' communication) and noV more liquid is available forpermitting-the pump to increase pressure on the left side of the plug 23. The plug. 23 then ceases to move further tothe right and balanced conditions prevail between the pressure on its left side and the pressure in biased spring 3i. 'I'he pressure at which the balanced condition occurs may be controlled from member 2l.

. If pressure is released from the tank T to its work circuit or elsewhere, pressure is accordingly reduced on the left side of the plug 23 which moves to the left under the resulting unbalance of spring 3|. This reconnects the ports ST and PS so that when the pump again comes into operation liquid is available for building up pressure in the tank T and thus also for resetting the plug 23 to covering position with respect to the ports I3.

On the other hand, when the pressure builds up too high and above said chosen moderate or normal value, for some accidental reason, excess pressure on the left side of the plug 23 finally forces it to uncover the port I3 (Fig-4) but since the plug itself at this time obstructs the right end of passage 1, it prevents a supply of liquid from entering the suction side of the pump, that The extending portion to the left of the plug 23 acts as a guide extensionv for the plug, being ground flat on one or two sides, as at 22, up to a shoulder; the nat portions affording passage for escape of uid when acting as a safety valve.

The area of the plug 23 exposed to pressure from the pressure port PP and acting as an abutment is calculated to balance the forces of spring 3 1 under the desired conditions of pressure in the tank T. The cylindric portion of the plug 23, which engages the cylindric passage 1, con-y stitutes a slide valve mechanism. After the device is installed, should it be desired to make adjustments inthe pressure to be maintained in the tank T, this may be done by adjusting the plug 28 by means of a suitable spanner wrench in openings 30. Adjusting ther plug 28 to the left will result inincrease of normal pressure in the tank T, and to the right, pressure decrease.

From the above, it will be seen thatthe device brings about a new fluid control circuit in which there is always a pressure connection between the pump P and pressure tank T. There is also f a suction connection between the pump and the ,sump tank S which is normally open itself and blocked from the pressure connection by plug valve 23 in the interconnection 1 (Fig. 2). Un-

der predetermined pressure the suction connec-A the block in the interconnection. 4The letter connects the pressure side of the pump with the sump tank S.

In view of the above, it will be seen that the As many changes could be made in the above constructions without departing Yfrom the scope v of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. A hydraulic system comprising in combination a liquid storage sump, an accumulator for storing liquid under pressure, aApressure-developing pump having an inlet connection normally in communication with the sump and a discharge connection normally in communication with the accumulator, a check valve arranged toxprevent reflux from the accumulator to said discharge connection, and a combined unloader and relief valve mechanism comprising a movable abutment subject to the pressure in the discharge connection between the pump and the check valve, yielding means reacting upon said abutment in opposition to discharge pressure, and a valve mechanism arranged to be actuated by said abutment and controlling communication bet-ween'the sump and the pump inlet connection and between the pump discharge connection and the sump, said valve mechanism assuming' a nor? mal position unless the pump discharge pressure exceeds a chosen value and in which the sump is connected with the pump inlet and isolated from the pump discharge, and assuming an unloading position when said pressure moderately exceeds said chosen value andin which said sump is disconnected from pump inlet and discharge, and which assumes a relief position when said pressure substantially exceeds said chosen value and in which the sump is disconnected from the pump inlet and connected with the pump discharge. 2. A hydraulic system comprising in combination a liquid storage sump, an accumulator for storing liquid under pressure, a pressure-developing pump having an'inlet connection normally in communicationl with the sump and a discharge connection normally in communication with the accumulator, a check valve arranged to prevent'reiiux from the accumulator to said discharge connection. and a combined unloader and relief valve mechanism comprising a movable abutment subject to the pressure in the dis- 'charge connection-between the pump and the -said abutment and controllingucommunication between `the sump and the pump inlet connection and between the pump discharge connection and the sump, said valve mechanism assuming a normal position unless the pump discharge pressure exceeds a chosen value and in which the sump is connected with the pump inlet and isolated from the pump discharge, and assuming an unloading position when said pressure moderately exceeds said chosen value and in which said sump is disconnected from pump inlet and discharge, and which assumes a relief position when said pressure substantially exceeds said chosen value and -in which the sump is disconnected from the pump inlet and connected with the p ump discharge, said valve mechanism comprising a cyconnected with the pump inlet and the pump discharge respectively, and said valve element comprising a cylindrical plunger subject onone end to pump discharge pressure and .on the other end to pump inlet pressure whereby the valve itself serves as the movable abutment, said valve having a mid position in which it disconnects the side port from the two end ports and two opponected with the sump, and opposite end ports site limiting positions in which respectively it with a sump tank, said control device having a connects the side port with one or the other of said end ports. A l V 3. A hydraulic control system comprising in combination an. accumulator pressure tank, a

sump tank, a pump having-a suction-pressure connection with the sump tank and a dischargepressure connection with the pressure tank, a

control device comprising a member having a cylinder in communication with said dischargepressure connection, a piston valve in said cylinder responsive yon one side to pressure in said discharge-pressure connection, a side inlet in said cylinder communicating with the sump tank and traversed by the valve, the cylinder having another opening on the suction-pressure side 'of f the piston val've forming a permanent communication between the valve and the suction side of the pump whereby the valve is at all times sub-- ject to pressure difference between its-pressure and suction sides, means biasing the valve to a normal position in response to normal pressure differences on its opposite ends wherein said side inlet is open and in communication with the' sump, said valve in response to moderate increase pressure on opposite ends to move beyond said side inlet to a point where 'the pump discharge connection is placed in communication with the sump.

r 4. In a pump circuit control, a control device forming a pressure passage connecting the pressure side of a pump with a pressure tank, said-v control device also forming part of a suction passage connecting the suction side of said pump cross passage connecting with the' pressure pasthe suction passage, means biasing the valve away from said intersection and toward a point to separate the pressure passage from the suction passage, said valve being responsive to a predetermined pressure va-lue in the pressure passage to move to the intersection-to block the sucin pressure diierences on opposite ends moving tionpassage' but initially without connecting said pressure and suction passages, said valve being movable inv response to greaterv pressure in the pressure passage to move to the other sideof the Aintersection whereby the pressure passage is connected to the sump tank without unblocking the 1 suction vpassagaand a .check valve in the pressure passage operable independently of said pis- Aton valve and arranged to close against backiiow from the pressure tank through said control device. y f

' HARVEY s. PARDEE. 

